In many land-based oil and gas drilling operations, drilling rigs are delivered to an oilfield drilling site by transporting the various components of the drilling rig over roads and/or highways and/or railroads. Typically, the various drilling rig components are transported to a drilling site on one or more truck/trailer combinations, rail cars, or other modes of transportation, the number of which may depend on the size, weight, and complexity of the rig. Once at the drilling site, the drilling rig components are then assembled, and the drilling rig assembly is raised to an operating position so as to perform drilling operations. After the completion of drilling operations, the drilling rig is then lowered, disassembled, loaded back onto truck/trailer combinations, rail cars, or other modes of transportation, and transported to a different oilfield drilling site for new drilling operations. Accordingly, the ease with which the various drilling rig components can be transported, assembled and disassembled, and raised and lowered can be a substantial factor in the drilling rig design, as well as the rig's overall operational capabilities and cost effectiveness.
Moreover, in particular parts of the world, access to cranes or other equipment for assembling and disassembling operations may be relatively limited and, in particular, the availability of large high lifting cranes may be limited. Where a large drilling rig with a high floor height is desired to provide for deep drill depths and high drilling capacities, the absence of large crane availability may create difficulties or impasses in assembly and disassembly of drilling rigs.
In some applications, drilling operations at a given oilfield drilling site may involve drilling a plurality of relatively closely spaced wellbores, sometimes referred to as “pad” drilling. In pad drilling, the distance between adjacent wellbores may be as little as 20-30 feet, or even less, and are oftentimes arranged in a two-dimensional grid pattern, such that rows and columns of wellbores are disposed along lines that run substantially parallel to an x-axis and a y-axis, respectively. In such pad drilling applications, after drilling operations have been completed at one wellbore, the drilling rig may be moved to an adjacent wellbore.
In light of the above, there is a need in the art for a drilling rig that can be assembled from relatively lightweight components with low heights while also providing for a rig that has a high floor height, a high capacity, and an ability to be moved for pad drilling operations.